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Figure 1. Maxwell’s portrait from the 1882 printing of the Life scanned from a copy owned by the present author.
correspondence and publications pertaining to molecules, gases, and related issues along with summaries of selected subsequent developments (Garber et al., 1986, 1995); and (4) partial compilations of Maxwell’s scientific correspon- dence and additional publications and manuscripts (Har- man, 1990, 1995, 2002). The chronology of Maxwell’s life and some relevant developments may be summarized as follows:
• 1831 (June 13): born in Edinburgh, Scotland
• 1847–1850: studies at the University of Edinburgh
• 1850–1856: enrolls in Cambridge University and
remains there after his first degree in 1854
• 1856–1860: holds the chair in Natural Philosophy,
Marischal College, Aberdeen, Scotland
• 1858: weds Katherine Mary Dewar; they have no
children
• 1860–1865: holds the professorship in Natural
Philosophy, King’s College London
• 1865–1871: retires from King’s College London, at
least partially for reasons of health, and typically
resides at his rural home in Glenlair, Scotland
• 1871–1879: holds the professorship in Experimental
Physics at Cambridge
• 1879 (November 5): dies of painful stomach cancer
• 1879 (December)–1884: Rayleigh holds the
professorship in Experimental Physics, Cambridge
Electromagnetic Theory and Waves
Maxwell’s progression of research resulting in the electro- magnetic wave theory of light may be summarized by his sequence of publications and insight provided from his cor- respondence (Marston, 2016). By 1855 and 1856, in his early papers, Maxwell had explored the usefulness of “physical analogies” between the motion of an incompressible fluid and Faraday’s electrical lines of force. He also showed how Faraday’s electromagnetic induction of currents and electric fields (E) could be expressed using a function he called by 1873 the vector potential (A). Expressed using modern no- tation, he found E = −∂A/∂t, where t denotes time.
By 1856, Maxwell had also developed a geometrical method for constructing diagrams of field lines. His series of papers in 1861 and 1862 developed an analogy of electrical vortices and electric particles for considering the coupled dynamics of electromagnetic fields, leading to his initial prediction of electromagnetic waves. These papers also introduced the notion of electromagnetic stresses (the Maxwell stress ten- sor) and of displacement currents. In his more famous pa- per (Maxwell, 1865), he derived the wave equation for the magnetic intensity (H) through the hypothesis of displace- ment currents without directly relying on a vortex analogy. In these papers, the predicted velocity of electromagnetic waves (hypothesized to correspond to light waves) de- pended on the ratio of certain electromagnetic quantities in absolute units. In the mid-1860s, Maxwell and associates made a significant effort to improve the accuracy of electri- cal measurements. One outcome was a new measurement of relevant electromagnetic quantities in 1868, giving addi- tional support to Maxwell’s electromagnetic theory of light. (By the mid-1880s, Rayleigh had located a systematic error in related properties of a standard for electrical resistance that improved the agreement with Maxwell’s theory of light [Strutt, 1924].) Maxwell examined in his Treatise (1873a) the measurement of electrical quantities and their physical significance along with a reformulation of electromagnetic theory. Two of the important results for the history of phys- ics were Maxwell’s diagram of the spatial relationship of electromagnetic fields in a propagation wave (Figure 2) and his prediction and analysis of optical radiation pressure.
In Article 830 of his Treatise, Maxwell expressed his confi- dence in the underlying assumptions of his electromagnetic theory of light. The Treatise, however, was difficult for stu- dents and Maxwell’s contemporaries to understand, in part because of Maxwell’s use of notation associated with quater-
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